st: small problem with povdeco

Dear Stata-listers,
Some must have asked this before, but I cannot find the thread on the Stata archives.
I am just using the command povdeco and would like a decomposition of the results by region.
povdeco r92pcex1 if urban2==0, pline(1160.363) by(reg7)
However, the programme stops and does not perform the decomposition by subregion.
varlist not allowed
r(101);
Does someone known why this is so ? (I am still using Stata7)
Thanks a lot,
Thi Minh
==================================================
Total number of observations = 3839
Weighted total no. of observations = 3839
Number of observations poor = 2428
Weighted no. of obs poor = 2428
Mean of r92pcex1 amongst the poor = 792.107
Mean of poverty gaps (poverty line - r92pcex1) amongst the poor = 368.256
Foster-Greer-Thorbecke poverty indices, FGT(a)
----------------------------------------------
All obs | a=0 a=1 a=2
----------+-----------------------------------
| 0.63246 0.20072 0.08492
----------------------------------------------
FGT(0): headcount ratio (proportion poor)
FGT(1): average normalised poverty gap
FGT(2): average squared normalised poverty gap
varlist not allowed
r(101);
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